Line protector having gas tube surge arrestor

ABSTRACT

A line protector has a gas tube surge arrestor through which overvoltages of short duration are grounded. The protector also includes a cap, a shunt within the cap and having circumferentially disposed, axially extending fingers projecting from one end of the cap, and a spring within the cap and pressing against an end of the shunt. The fingers retain the gas tube assembled with the shunt and have extremities externally of the tube and intermediate the electrodes of the gas tube. The shunt electrically contacts one of the electrodes. The shunt also has radial ledges for supporting the gas tube in opposition to the force of the spring. A solder pellet may be interposed between said one electrode and the ledge so that upon melting of the solder pellet due to an overcurrent condition in the line, at least one of the extremities of the shunt will engage the other electrode externally of the tube and cause a direct metallic circuit from the line to ground.

United States Patent [:91

Klayum LINE PROTECTOR HAVING GAS TUBE SURGE ARRESTOR [75] Inventor: Milton A. Klayum, Itasca, Ill.

[73] Assignee: Reliable Electric Company, Franklin Park, 111.

[22] Filed: Feb. 4, 1974 [21] Appl. No.: 439,348

[52] U.S. Cl. 317/62; 317/66; 337/32 [51] int. Cl. H02h 9/06 [58] Field of Search 317/66, 61.5, 69, 61, 62; 337/15, 32, 33

[56] References Cited UNITED STATES PATENTS 2,724,793 11/1955 Fisher 317/66 3,703,665 11/1972 Yereance et al 317/61 3,755,715 8/1973 Klayum et al 317/66 Primary Examiner-James D. Trammell Attorney, Agent, or FirmO1son, Trexler, Wolters, Bushnell & Fosse [451 May 27, 1975 [57] ABSTRACT A line protector has a gas tube surge arrestor through which overvoltages of short duration are grounded. The protector also includes a cap, a shunt within the cap and having circumferentially disposed, axially extending fingers projecting from one end of the cap, and a spring within the cap and pressing against an end of the shunt. The fingers retain the gas tube assembled with the shunt and have extremities externally of the tube and intermediate the electrodes of the gas tube. The shunt electrically contacts one of the electrodes. The shunt also has radial ledges for supporting the gas tube in opposition to the force of the spring. A solder pellet may be interposed between said one electrode and the ledge so that upon melting of the solder pellet due to an overcurrent condition in the line, at least one of the extremities of the shunt will engage the other electrode externally of the tube and cause a direct metallic circuit from the line to ground.

9 Claims, 4 Drawing Figures LINE PROTECTOR HAVING GAS TUBE SURGE ARRESTOR BACKGROUND OF THE INVENTION This invention relates to improvements in line pro tectors for communications circuits, such as telephone lines and the like.

More particularly, the present invention is concerned with protectors of the type intended for protection of wire conductors and equipment connected thereto from electrical overvoltage and overcurrent conditions which may result from electrical power faults, lightning, and the like. In many instances it is desirable that the protector have a so called fail-safe operation. By this it is meant that the protector should provide a direct metallic current path from the line to the ground in the event of an overcurrent condition which would tend to damage the protector. Where a gas tube surge arrestor is used in the protector, the provision of a failsafe mode of operation external to the gas tube is highly desirable.

One satisfactory approach to providing an external fail-safe mechanism in a protector embodying a gas tube surge arrestor is shown and described in US. Pat. No. 3,755,715 that issued Aug. 28, 1973. The protector shown therein relates to a heavy duty or medium duty protector. There are, however, certain areas of need for lighter duty and less costly arrangements than is shown in the aforesaid patent. Thus, the larger number of parts present in the unit of the aforesaid patent may be justified for heavy and medium duty use, but this is not the case where the cost of the protector is the primary consideration.

OBJECTS AND SUMMARY OF THE INVENTION It is the object of this invention to provide a line protector of the general type and for the purpose stated that embodies a gas tube surge arrestor for protecting the line against overvoltage faults, and wherein the protector is of relatively simple and inexpensive construction.

A further object of this invention is to provide a line protector of the type stated which embodies a mechanism for effecting a fail-safe operation in the event of an overcurrent line fault. This fail-safe arrangement provides for a direct metallic current path from the line to ground, bypassing the arrestor.

A more specific object of this invention is to provide, in a line protector of the type stated, a novel shunt member that permits the use of only a small number of parts in the protector.

In accordance with the foregoing object, an embodiment of the invention comprises agas-filled tube of the cold cathode type and having opposed electrodes forming an arc gap. The protector also includes a tubular cap and a spring within the cap. A shunt is telescoped within the cap and has fingers in conductive engagement with the cap, the fingers having extremities outside of the cap. The shunt is in conductive connection with only one of the electrodes of the gas tube. The spring imposes axial pressure on an end of the shunt within the cap. The extremities of the fingers are external of the gas tube and are positioned axially intermediate the two electrodes and retain the gas tube assembled with the shunt. The shunt also has radial ledge portions between the end of the shunt that are engaged by the spring and the finger extremities. Optionally a solder element may be interposed between the ledge portions and said one electrode. If an overcurrent condition causes the solder element to melt, at least one of the extremities of the fingers engages the other electrode of the gas tube to form a direct metallic current path from said other electrode to the cap. Said other electrode and the cap are respectively connected to the line to be protected and to ground or vice-versa. Typically, the cap with the assembled spring, shunt, gas tube arrestor and solder element (if used) may be readily installed as a unit into a mounting block of conventional design.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a sectional view taken substantially through the central axis of a line protector constructed in accordance with and embodying the present invention, the protector being shown in its normal operating condi' tion and being mounted in a block or base assembly;

FIG. 2 is a perspective view of the shunt which forms part of the present invention;

FIG. 3 is an exploded side elevational view, partially in section, of the protector; and

FIG. 4 is a sectional view, similar to FIG. 1, but showing the condition of the protector after the latter has been subjected to an overcurrent condition that causes the solder element to melt.

DETAILED DESCRIPTION Referring now in more detail to the drawing there is shown a line protector 2 that comprises a sheet metal tubular cap 4 having an annular radial flange 6 that is axially spaced from the end wall of the cap. The cap 4 also has a cylindrical wall that is formed with a thread 8, and an axially extending cylindrical skirt' 10 that is adjacent to the thread 8. The skirt l0 terminates in the open end of the cap 4.

Telescoped within and coaxial with the annular skirt 10 is a metallic cage or shunt 12. The shunt 12 is a onepiece member having cylindrical end wall 14 and a series of circumferentially spaced, generally axially extending fingers 16. In the present form of the invention four fingers 16 are shown and each are ninety degrees apart and project from the periphery of the end wall 14. The fingers 16 have respective extremities 18 which may be of the generally V-shaped configuration shown. Also provided on the shunt 12 are secondary fingers 20 which are also four in number and which are alternately disposed between respective fingers 16. These secondary fingers 20 are shorter than the fingers l6 and also project from the periphery of the end wall 14. At the ends of the secondary fingers 20 that are remote from the wall 14 there are radial ledges 22, one being joined to each of the secondary fingers 20. These radial ledges 22 are generally parallel to and axially spaced from the end wall 14 a requisite amount for reasons presently more fully appearing. Furthermore, the ledges 22 are somewhat sector shaped, departing therefrom by arcuate inner edges which define an opening 24. The sides of the ledges 22 extend radially from the opening 24 to define generally V-shaped spaces 26 between adjacent ledges 22.

Disposed within the shunt 12 substantially coaxial therewith is a gas tube surge arrestor 28 of known design. Suffice it to say, however, that the gas tube comprises a glass cylinder 30 having opposed, generally concave electrodes 32, 34 bonded to opposite ends thereof. The facing surfaces of the electrodes 32, 34 that are within the sealed gas tube arrestor 28 define an arc gap 36. The electrodes 32, 34 also include radial rims or flanges 38, 40 which project radially beyond the outer diameter of the cylinder 30. The gas tube arrestor may be filled with any suitable inert gas and may also include a radioactive substance therein.

Axially interposed between the ledges 22 and the electrode flange 40 is a fusible material, such as a solder pellet 42. The solder pellet may be of a low melting point metal, for instance, an alloy having a melting point in the range of 185 to 300 F. The solder pellet 42 is essentially a cylindrical disc which has an end surface engaging and supported by the large area of the ledges 22. Positioned axially within the cap 4 is a coil compression spring 44, one end of which engages the end wall of the cap 4 and the other end of which bears against the end wall 14 of the shunt 12. The force of the spring 44 is transmitted through the secondary fingers 20 to the ledges 22 which, in turn, apply force through the solder pellet 42 to the gas tube 28 at its electrode flange 40.

Prior to assembly of the components of the protector 2, as seen in FIG. 3, the resilient fingers 16 are spread apart further than in the assembled condition of the protector shown in FIGS. 1 and 4. In assembling the protector, the solder pellet 42 is placed on the ledges 22 after which the gas tube arrestor 28 is placed on the solder pellet 42. With the spring 44 in the cap, the shunt fingers 16 are grasped and the assembled unit consisting of the shunt, solder pellet and gas tube is telescoped within the cap skirt 10. The fingers 16 are moved radially inwardly, but since they are resilient they are in firm pressure engagement with the inside surface of the skirt 10. The clearances 26 prevent obstruction of the fingers 16 by the ledges 22. Furthermore, the fingers l6 tend to maintain the gas tube 28 and solder pellet 42 substantially coaxially with the shunt 12. It will also be seen that the extremities l8 radially overlap the electrode flange 40 to prevent axial movement of the flange 40 therepast. This retains the gas tube and shunt assembled. It is also important to note that in the assembled protector the extremities l8 lie axially intermediate the electrode flanges 38, 40 and spaced from the flange 38.

The protector 2 may be screw threaded into a well 46 of a dielectric mounting block 48. At the opening of the well there is a metallic contact plate 50 having an internally threaded annular flange 52 for receiving the thread 8 on the cap 4. The dielectric material of the block 48 may also be threaded axially beyond the flange 52 so that the cap may be threaded into the well 46 until the flange 6 abuts the contact plate 50. At the end of the well that is opposite to the contact plate 50 there is a contact strip 54 that is adapted to engage the electrode flange 38. The contact plate 50 and the contact strip 54 may be connected respectively in a known manner to ground and to the line to be protected. In any event, when the protector is threaded into the well 46 the engagement of the electrode 32 with the contact strip 54 causes the spring 44 to compress. The compression in the spring 44 maintains a firm contact between the assembled gas tube 28, solder pellet 42, and shunt 12. The compression of the spring 44 may cause the extremities 18 to move axially relatively to the electrode flanges 38, 40, but nevertheless the extremities 18 remain spaced from the electrode flange 38, a distance which is preferably less than the axial thickness of the solder pellet 42.

With the contact strip 54 connected electrically to the line to be protected there is a circuit that provides overvoltage protection from the line to ground. This circuit comprises, in series, the electrodes 32, 34 and the arc gap 36, the solder pellet 42, the shunt l2 and the cap 4. Overvoltages cause a breakdown of the gas tube resulting in an arc across the gap 36, which is discharged to ground. If there is an overcurrent fault on the line sufficient to melt the solder element 42, as is shown in FIG. 4, the spring 44 pushes the shunt 12 axially so that at least one if not all of the extremities 18 engages the electrode flange 38. This provides a direct metallic path from the contact strip 54 through the shunt l2 and through the cap 2, bypassing both the arc gap 36 and the coil spring 44.

The relatively large area provided by the ledges 22 results in more than half of the end surface of the solder 42 being supported by the shunt 12. As a result, there is little tendency for the solder pellet 42 to be subjected to a cold flow under pressure from the spring 44, which would prematurely cause the line to be grounded.

Upon melting of the solder pellet 42 the protector 2 can be unscrewed from the well 46. The entire protector may be disassembled readily and the necessary parts replaced.

As suggested above, the arrestor can be made without the solder pellet 42 in those instances where the solder pellet is not needed or is not desired by the user. In such case, the shunt 12 can be fabricated with the lengths of the secondary arms 20 being somewhat longer so that the ledges 22 directly engage the electrode flange 40.

The invention is claimed as follows:

1. A line protector comprising means forming a circuit that is adapted to be connected between a line and ground to provide overvoltage protection for the line, said circuit comprising, in series, spaced electrodes forming an arc gap and being part ofa gas tube, a shunt having means forming an electrical contact with only one of said electrodes, and a tubular cap that telescopically and conductively receives said shunt coaxially therein; a spring in said cap and imposing axial pressure on said shunt in the direction of said gas tube, said shunt having fingers projecting in an axial direction from one end of said cap, said fingers having extremities axially between said electrodes exteriorly of said gas tube and normally out of contact with the other electrode, and said shunt having ledges axially intermediate said extremities and said spring and comprising said means for forming said electrical contact with said one electrode, said last-named means also providing a support for said gas tube at said one electrode.

2. A line protector according to claim 1 in which said ledges are generally radially extending, and said spring applies force through said ledges to said gas tube axially thereof.

3. A line protector according to claim 2 in which said shunt has an end wall in said cap for receiving the force from said spring, and said ledges are axially spaced from said end wall.

4. A line protector according to claim 3 in which said ledges are joined to said end wall by secondary fingers.

5. A line protector according to claim 4 in which the fingers and the secondary fingers project from the periphery of the end wall and are alternately disposed around said periphery.

6. Aline protector according to claim 1 in which said means forming the electrical contact with said one electrode includes a solder element axially interposed between said ledges and said one electrode such that an overcurrent condition on said line that causes said solder element to melt will cause said spring to urge at least one of said extremities into electrical contact with said other electrode to form, via said shunt, a direct metallic current path between said other electrode and said cap.

7. In a line protector having a gas-filled tube with opposed electrodes forming an arc gap, a threaded cap, a shunt within the cap and having fingers in conductive engagement with the cap, said fingers having extremities outside of the cap, said shunt also being in conductive connection with only one of said electrodes, and a spring imposing pressure on an end of said shunt within the cap; an improvement in which said fingers are external of the gas tube and between said electrodes, and said shunt having means for supporting said gas tube at said one electrode, said last-named means including radial ledge means axially between said end and said finger extremities.

8. In a line protector according to claim 7, a solder element forming part of said supporting means and interposed between said ledge means and said one elec trode.

9. In a line protector according to claim 7, said ledge means being secured to said shunt end by secondary fingers between the first-mentioned fingers.

* l i =l 

1. A line protector comprising means forming a circuit that is adapted to be connected between a line and ground to provide overvoltage protection for the line, said circuit comprising, in series, spaced electrodes forming an arc gap and being part of a gas tube, a shunt having means forming an electrical contact with only one of said electrodes, and a tubular cap that telescopically and conductively receives said shunt coaxially therein; a spring in said cap and imposing axial pressure on said shunt in the direction of said gas tube, said shunt having fingers projecting in an axial direction from one end of said cap, said fingers having extremities axially between said electrodes exteriorly of said gas tube and normally out of contact with the other electrode, and said shunt having ledges axially intermediate said extremities and said spring and comprising said means for forming said electrical contact with said one electrode, said last-named means also providing a support for said gas tube at said one electrode.
 2. A line protector according to claim 1 in which said ledges are generally radially extending, and said spring applies force through said ledges to said gas tube axially thereof.
 3. A line protector according to claim 2 in which said shunt has an end wall in said cap for receiving the force from said spring, and said ledges are axially spaced from said end wall.
 4. A line protector according to claim 3 in which said ledges are joined to said end wall by secondary fingers.
 5. A line protector according to claim 4 in which the fingers and the secondary fingers project from the periphery of the end wall and are alternately disposed around said periphery.
 6. A line protector according to claim 1 in which said means forming the electrical contact with said one electrode includes a solder element axially interposed between said ledges and said one electrode such that an overcurrent condition on said line that causes said solder element to melt will cause said spring to urge at least one of said extremities into electrical contact with said other electrode to form, via said shunt, a direct metallic current path between said other electrode and said cap.
 7. In a line protector having a gas-filled tube with opposed electrodes forming an arc gap, a threaded cap, a shunt within the cap and having fingers in conductive engagement with the cap, said fingers having extremities outside of the cap, said shunt also being in conductive connection with only one oF said electrodes, and a spring imposing pressure on an end of said shunt within the cap; an improvement in which said fingers are external of the gas tube and between said electrodes, and said shunt having means for supporting said gas tube at said one electrode, said last-named means including radial ledge means axially between said end and said finger extremities.
 8. In a line protector according to claim 7, a solder element forming part of said supporting means and interposed between said ledge means and said one electrode.
 9. In a line protector according to claim 7, said ledge means being secured to said shunt end by secondary fingers between the first-mentioned fingers. 